This invention relates, in general, to a dental implant for use in maxillo-facial surgery; and, in particular, to a juxtaosseous implant universally applicable at an implantation site on the mandible or maxilla, and to a method of surgical implantation using such an implant.
A dental implant of the type to which the present invention relates is intended to function as a bond between a dental prosthesis, such as a crown or bridge, and one of the mandible and maxilla facial bones. It is normally desired that such bond be permanent. A dental implant is subject to many varied and frequent stresses, often of considerable magnitude. So it is important that the connection between the implant and the bone be strong and secure.
Long term success of the bone-to-implant connection requires good biological acceptance resulting in tissue scarification, as well as good biomechanical adaptation resulting in consolidation. The desired result is a stable and sufficiently strong mounting taking into account the maxim in bone surgery that: "the stability of a mounting is indispensable for the formation of good bone callus; and, conversely, good bone callus ensures good stability." Failure in about 15% of dental implants is synonymous with osteolysis.
As a dental implant is intended to replace the natural bond between a tooth and the bone, it must be able to withstand the same stresses to which the natural connection between a tooth and the bone would be subjected. The stresses derive from forces applied through the prosthesis onto the implant which transmits them to the bone. In order to obtain good consolidation, it is desirable that the stresses transmitted to the bone by the implant be as close to normal as possible in order to avoid disadvantageous restructuring of the bone in adherence to Wolf's law. To avoid parasitic stresses, the dental implant should also not have any abnormal mobility. Thus, it is desirable that the implant have a stable, or even better, a hyperstable, seating from the onset. This means that the implant should be designed for immediate adequate permanent placement. Furthermore, taking into account the interaction between the bone and the implant, research has shown that good quality bone callus makes it desirable for the pericortex and the implant to constitute a coherent mechanical entity.
As with other bones, the mandible and maxilla each have two types of bone tissue: the cortical and the cancellous. The cortical bone is the hard and compact external casing that has a dense structure composed of osteons assimilable to fibers. The cancellous or trabecular bone is soft and spongy, and covers the internal faces of the cortical bone. Cancellous bone is made of superimposed lamellae, comparable to plywood.